1. Field of the Invention
The present invention relates, in general, to a catalyst injection nozzle for a high-pressure chemical reactor such as an autoclave reactor for polymerizing ethylene into polyethylene. More particularly, the present invention is directed to an improved catalyst injection nozzle for spraying liquid catalyst in a finely atomized state into a high-pressure chemical reactor vessel.
2. Discussion of the Prior Art
Various types of high pressure chemical reactors have been developed in the chemical arts in which catalytic agents are injected into an ongoing chemical reaction to secondarily promote the reaction. One technical area in which reactors of this type are utilized is in the polymerization of a monoolefin such as ethylene into a polymer. A reactor of this type is described in Pugh et al. U.S. Pat. No. 3,756,966 granted to National Distillers and Chemical Corporation on Sept. 4, 1973, and more recently in Platz et al. patent application Ser. No. 714,451 filed Aug. 16, 1976 for Ethylene Polymerization Reactor, now U.S. Pat. 4,071,325 issued Jan. 31, 1978, also assigned to National Distillers and Chemical Corporation.
In autoclave reactors of this type, catalyst is injected into the reaction mixture at various entry ports along the length of the reaction vessel. The successful operation of the polymerization process is often critically dependent upon the accurate and reproducible uniform injection of given quantities of catalyst into the chemical reaction. It is desirable that the catalyst be dispersed to the greatest possible extent throughout the reaction materials such that the catalyst promotes the polymerization process in a uniform manner throughout all of the materials. An effective dispersal of the catalyst avoids the formation of hot spots in the mixture which may be caused by concentrations of catalyst at different locations within the reaction materials.
Liquid catalysts suitable for use in reactors of this type include highly oxygenated agents such as peroxide catalysts which give up oxygen at the elevated temperatures which are present in autoclave reactors.
U.S. Pat. No. 4,002,813 to Steinert et al. discloses a catalyst injection system for the polymerization reaction of a monoolefin, such as ethylene, in which the catalyst stream is delivered to the reaction vessel through a separate infeed conduit. The infeed conduit terminates in an orifice tip which is located within and is substantially coplanar with the entry port of the monomer stream into the reaction vessel. This arrangement results in the catalyst being injected into the reaction vessel in the midst of the monomer stream as it is fed to the reactor. A drawback of this system lies in that it does not produce a widespread dispersal of the catalyst within the reaction mixture.
U.S. Pat. No. 3,738,976 to Heavin discloses a system for introducing a catalyst slurry into the polymerization zone of a reactor in which the catalyst slurry is pressurized by passage through a transport zone. The transport zone includes an orifice which is closed by a spring-biased element so that a given pressure differential must be maintained across the orifice before catalyst is injection sprayed into the reaction zone. This catalyst introduction system is designed for low pressure reactors, with the pressures referred to in the patent being at about atmospheric or somewhat higher. The catalyst introduction system described in Heavin includes an axially movable shaft for opening and closing the catalyst injection aperture. The shaft extends through a wall of the reactor to a spring positioned outside thereof, and with a plurality of packing rings being placed around the shaft in order to seal the reactor. Packing rings of this nature, although effective in low pressure environment, generally will not function properly in a high pressure reactor of the type for which the present invention has been designed, and would result in the leakage of reactant materials past the shaft. Even if the packing rings were to be replaced by another type of sealing arrangement, there would always be sealing problems due to the inherent nature of the Heavin design in which an axially movable shaft for controlling the catalyst injection aperture extends through the reactor wall. This arrangement must allow for axial movement of the shaft while requiring the sealing over a tremendous pressure differential present along the shaft.
Smith U.S. Pat. No. 2,035,203 to Smith discloses a spray nozzle for dispersing a fuel to an internal combustion engine in an atomized spray. In this instance, the spray is injected through a plurality of discrete orifices rather than uniformly, so as to render the nozzle structure unsuitable for the injection of an atomized spray of a liquid catalyst into a high-pressure chemical reactor.
In view thereof, a new design for a catalyst spray nozzle is required which allows for the introduction of an atomized spray of liquid catalyst into a high pressure reactor with pressures commonly exceeding 20,000 psi, and which functions effectively without undue danger of a leak of reaction materials by the catalyst spray injector nozzle, as might be incurred in a catalyst spray injector design of the type disclosed in the prior art.